The design of catheters and catheter systems for use in coronary angioplasty has previously been an exercise in compromise. To gain the benefit of some features, others had to be sacrificed. As a result, the design of percutaneous transluminal coronary angioplasty (PTCA) balloon catheters has moved toward the direction of single-feature niche products. For example, in very tight lesions where profile is the priority feature, balloon-on-wire catheters, which have lower profiles, are commonly used. To gain the low profile feature, steerability has been compromised and the ability to exchange catheters has been sacrificed. Monorail and over-the-wire PCTA systems provide exchangeability, but these systems are larger than the balloon-on-wire catheters. Attempts to make these systems smaller have been at the expense of steerability, pushability, trackability, and balloon deflation time. The challenge of incorporating all the features desired by the interventional cardiologist within the boundary that the device be as small as possible has been described as "trying to put ten pounds of stuff in a five pound bag." A means to accomplish this objective would be to have a catheter device in which the shaft diameter could be varied during the procedure.
Catheters having variable diameters are known in the literature. Fuqua, U.S. Pat. No. 4,601,713 discloses a variable diameter catheter where the catheter is folded in a longitudinal manner to reduce its diameter. The folded catheter is held within a separate retaining means to maintain its folded state. Thus, a separate retaining means is required.
According to Saab, U.S. Pat. No. 4,800,349, an over-the-wire balloon dilatation catheter has a collapsible sleeve and balloon at its distal end. The flexible, non-collapsible inner shaft has a smaller diameter at its distal end, and its larger proximal end contains an inner lumen and a balloon inflation lumen. The sleeve is disposed concentrically around the smaller distal portion of the shaft, and the annular space between said distal portion and the sleeve is in fluid communication with the balloon inflation lumen of the shaft.
Despite the advances represented by the above-described patents, there is still a need for a simplified, easy-to-manufacture variable diameter shaft balloon catheter, especially one having better, inherent steerability.